The present invention concerns data centres and a method of cooling equipment in a data centre. The invention also concerns apparatus for cooling a data centre.
A data centre is a late 20th Century development that has grown as a response to the increasing demand for computer processing capability and a recognition of the importance of information technology (IT) in the place of every business and organisation today. Whereas smaller organisations have sufficient processing power with laptops, PCs and occasionally servers, larger organisations require higher capacity centralised processing to serve a wide range of needs and applications. A few years ago this capacity was supplied by large mainframe computers, but more recently the method used has been to provide data centres comprising many networked computer servers known as “blades” installed in racks enabling controlled and modular expansion of capacity. The racks also typically house storage systems and/or telecommunications equipment such as routers to handle data flow between the computer servers and data flow between the data centre and the outside world.
One key problem faced is how to cool a data centre effectively and efficiently. In a traditional data centre arrangement the racks are laid out in rows. Cooling is provided by direct expansion (DX) or chilled water cooling plants. The cool air produced by these units is entrained through an underfloor plenum and exits through floor grilles at the front of the IT rack rows. The IT products installed in the racks contain integral fans which draw the cooled air from the front across the circuitry and heat is exhausted via vents in the products to the rear. In certain arrangements of the prior art, the separation between these IT racks creates a ‘hot aisle’ into which air is expelled by the IT products in the racks and a ‘cold aisle’ from which cooler air is drawn into and through the IT products by their integral fans.
A typical arrangement of the prior art is shown schematically in FIG. 1 of the attached drawings. Thus, the data centre includes a rack room 1 defined by walls 2 in which two sets of racks 4 for IT equipment are accommodated. The IT equipment in the racks 4 generate heat, represented by arrows 6. The cooling of the IT equipment is achieved by introducing cold air, via a floor void, into the room by means of air conditioning units, the cold air being represented by arrows 8.
In certain data centre arrangements it is important that the volume of cold air supplied is equal to or greater than that drawn through the servers by their internal fans. If the volume is not sufficient, then the servers can draw in warm air from other areas of the data centre, possibly resulting in the IT equipment overheating. In a traditional data centre this is generally avoided by supplying significantly more cold air than the servers actually need at any given time. It will be seen that this typical data centre arrangement is not particularly energy efficient.
The drive for more efficient use of power has given rise to a need to make the cooling regimes used in data centres more efficient, as cooling of equipment typically contributes significantly to the power used by a data centre. For example, the power usage in certain data centres may require between 1 kW and 2 kW of power for every 1 kW of power used to power the IT equipment, a significant proportion of which would be related to cooling.
In recent years, data centre designers have sought to improve energy efficiency with cooling systems that attempt to tailor the amount of cooling air delivered to the actual requirements of the servers at any given time. U.S. Pat. No. 6,283,380 (IBM), for example, describes a system for automatically controlling the volume and distribution of cooling air supplied to IT equipment in a data centre based on the data provided by a network of temperature sensors deployed at various positions around the rack room. The temperature data is input into a computer simulation of the rack room and the predictions of this simulation are used to adjust the speed of the fans supplying the cooling air. This system has the disadvantages that it requires a significant number of both fans and temperature sensors to be distributed around the data centre in order to achieve effective airflow control, and the simulation uses significant computing power.
An alternative method is to measure the pressure in the “cold aisle” area at the front of the racks and to adjust the amount of cold air supplied from the CRAC unit so as to maintain a constant pressure. The pressure at the front of the racks will vary according to whether the amount of cold air being supplied is too much or too little to meet the demand of the servers. If too much cold air is supplied, the pressure will increase, whereas if too little is supplied it will decrease. Keeping the pressure constant therefore means that the amount of cold air supplied by the CRAC unit is appropriate to the demand of the servers at a given time.
U.S. Pat. No. 6,694,759 (Hewlett Packard) provides an example of this method in which pressure measurements are also used to adjust the vents through which the cold air exits a cold air plenum, providing an extra level of control over the airflow. As this document explains, however, the pressure within the rack room and within the plenum is highly non-uniform, and fluctuates unpredictably. As such, a complex network of sensors and vents is required in order to provide adequate airflow control.
Efforts to improve energy efficiency by separating the flows of hot and cold air in a data centre have also become popular recently. This may be done by, for example, adding baffles across the top of the hot and/or cold aisles, with doors or further panels across the end of the aisle. A baffle arrangement is for example proposed in WO 2006/124240 (APC). In data centres where the hot aisles and/or the cold aisles are enclosed, the pressure differential between the front and rear of the racks can be larger than the situation where the hot and cold aisles are not sealed off from one another. In such data centres if the pressure in the cold aisle becomes lower than the pressure in the hot aisle, warm air from the hot aisle can be drawn back through the servers since all other air paths are blocked. This situation is likely to lead to the servers overheating. In data centres with encapsulated hot and/or cold aisles, it is therefore even more important to ensure that the pressure in the cold aisle is always greater than that in the hot aisle. GB2466178 (Hewlett Packard) (filed earlier but published later than the earliest claimed priority date of the present application) describes a method of monitoring this pressure differential in a data centre where the cold aisles are supplied with cooling air from an underfloor plenum, which involves measuring the air flow velocity through a small opening between a hot aisle and a neighbouring cold aisle.
A further way of improving the energy efficiency of a data centre is to use cool air from outside the data centre for cooling the IT equipment (known in the art as free cooling) whenever the ambient conditions allow, and/or using adiabatic cooling instead of mechanical cooling. WO2010/075358 (Amazon Technologies) (filed earlier but published later than the earliest claimed priority date of the present application), for example, describes a data centre cooling system having both mechanical and adiabatic cooling apparatus, which can be operated in various modes utilising combinations of adiabatic, mechanical and free cooling depending. A disadvantage of prior art combined systems such as that of WO2010/075358 is that although they control what type of cooling apparatus is used depending on ambient air conditions, they are not sophisticated enough to be able to tailor the interaction of the various types of cooling apparatus so as to achieve optimum, or close to optimum, efficiency.
The present invention seeks to provide an improved method and apparatus for cooling a data centre. Alternatively or additionally, the present invention seeks to provide a system for cooling a data centre that mitigates one or more of the above mentioned disadvantages.